Companion command line window on Windows

[rolandhill]

Hi All,

I was wondering if other people get a companion command window opening with their VSG application on Windows? If, for example, you double click the vsgdraw example in file manager, you first get a command line window, then the VSG graphics window opens as well. The same thing happens for my own application. This doesn't happen in Linux. Does anyone know how to prevent the companion window from opening?

Thanks,
Roland

[robertosfield]

As I'm not a regular Windows user I had to do a quick search online, and this StackOverflow entry looks most appropriate:

https://stackoverflow.com/questions/18260508/c-how-do-i-hide-a-console-window-on-startup

It looks like either calling ShowWindow to hide the console:

::ShowWindow(::GetConsoleWindow(), SW_HIDE);

Or linking the application with -mwindows.

Hopefully actual Windows experts can chime in here...

[AnyOldName3]

There's a linker flag /SUBSYSTEM on Windows that determines whether your application uses the command-line subsystem (where the entrypoint for the application is main and standard streams are preconfigured) or the Windows subsystem (where the entrypoint is WinMain and you need to explicitly configure the standard streams). It also controls whether a terminal window is spawned automatically if the parent process doesn't provide one.

For a CMake project, this is controlled by the WIN32_EXECUTABLE target property, which can be set by:

• setting the property explicitly on a target after it's been declared.
• setting the CMAKE_WIN32_EXECUTABLE variable before the target's declared.
• passing WIN32 to the add_executable call for the target.

It's better to do this than to pass the linker flags explicitly as the linker flag that controls this is different for different compilers (e.g. /SUBSYSTEM:WINDOWS for MSVC/clang-cl or -mwindows for MinGW's GCC and Clang) and CMake can handle this for you automatically.

If you need std::cout etc. to work for a Windows subsystem application, then it can be a bit of a hassle to set it up. They'll be fine if they've been redirected to a file or a pipe, but won't show up in a parent console until you:

• check there's a parent console with GetConsoleWindow()
• check the streams aren't already redirected by comparing GetFileType(GetStdHandle(STD_OUTPUT_HANDLE)) etc. to FILE_TYPE_DISK and FILE_TYPE_PIPE - you want to leave them alone if they're either of these types
• attach to the parent console with AttachConsole(ATTACH_PARENT_PROCESS)
• flush the output streams
• reopen stdin, stdout and stderr with freopen so they're connected to the special file called CON.

If you don't need to write any console output, then setting WIN32_EXECUTABLE in CMake will do what you want and you can skip the rest.

[rolandhill]

Thanks so much for your help!

I had previously tried to add the linker option for Windows builds in Cmake using
add_link_options(/SUBSYSTEM:WINDOWS)

It didn't solve the problem. So taking your advice I've let CMAKE do the hard work. I'm writing for Linux and Windows (with Mac to follow) and I want to be able to pass in command line options. The Solution that worked for me is:

1. Add a line in CMAKE setting CMAKE_WIN32_EXECUTABLE before declaring the project

cmake_minimum_required(VERSION 3.7)

set(CMAKE_WIN32_EXECUTABLE ON)

project(si
        VERSION 2.3.3
        DESCRIPTION "Spatial Integration (alpha)"
        LANGUAGES CXX
)

2. Windows now expects the entry point to be WinMain(), so

#if defined(_WIN32)
int WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow)
#else
int main(int __argc, char *__argv[])
#endif
{
      siApp app;
      if(app.init(__argc, __argv))
      {
          app.run();
          app.close();
      }
}

Both Linux and Windows work and there is no more command line window in Windows (smiley face).

Cheers,
Roland

[robertosfield]

Good to hear you've found a solution, even if it is a bit more hacky than it should all because, well Microsoft love corrupting standards...

Another workaround that might be worth trying is redirecting std::cout and std::cerr to the vsg::Logger and registering a logger than passes stuff on to Windows reporting system. From vsgviewer.cpp:

        // if we want to redirect std::cout and std::cerr to the vsg::Logger call vsg::Logger::redirect_stdout()
        if (arguments.read({"--redirect-std", "-r"})) vsg::Logger::instance()->redirect_std();